Stop us if you've heard this before: Dietary supplements are not regulated like prescription drugs. (Manufacturers are asked to report problems with their products but it's voluntary.) But the Food and Drug Administration and the Centers for Disease Control and Prevention have teamed up to figure out just how many people are heading to the emergency room as a result of these pills, powders, and chews.

In a study published in the New England Journal of Medicine, the FDA and CDC estimated that 23,000 ER visits annually are related to supplement use, with 2,100 of those resulting in hospitalization. (The study looked at data from 63 hospitals between 2004 and 2013, and extrapolated based on the U.S. population to reach that figure.) The authors noted that these numbers are likely underestimated, since people don't always cop to supplement use, and doctors may not ID them as the cause of a health problem like they might with a prescription drug.

More than half of the patients in the study were women. Among people 34 and younger, weight-loss and energy supplements were the biggest culprits, accounting for more than half of the ER visits in that group — many people presented symptoms like heart palpitations and chest pain. Heart symptoms were also common in people taking bodybuilding and sexual-enhancement products. Multivitamins and single-nutrient vitamins made the list as well, accounting for about 32 percent of all ER visits, mostly the result of allergic reactions.

"Natural" libido pills made the news earlier this week. After former Lakers player Lamar Odom collapsed on Tuesday, investigators learned that he had used cocaine and a sexual-enhancement supplement called Reload in the days before his hospitalization. But this so-called "herbal Viagra" was the subject of a stern FDA warning in 2013 because it contains the active drug in Viagra, sildenafil, which can interact with nitrates found in some prescription drugs and might lower blood pressure to dangerous levels. It's not listed on the label and skirts regulation since it's sold as a supplement. (It's not known if Odom was taking other medications and he remains on life support.)

The FDA does test some supplements, but the group told USA Today in 2013 that it had the budget to test 1,000 per year, and there are an estimated 85,000 on the market. And while authors note that ER visits for supplements are a fraction of those related to prescription drugs (just 5 percent), supplements are marketed "under the presumption of safety" since manufacturers aren't required to list side effects or possible interactions. Seems risk-free, right? The authors recommend telling your doctor about any supplement you take, and if you have underlying heart problems, they might tell you to toss certain ones.